// 判断子序列
/**
 * @param {string} s
 * @param {string} t
 * @return {boolean}
 */
 var isSubsequence = function(s, t) {
    let i=0,j=0;
while(i<s.length && j<t.length){
    if(s[i]==t[j])
        i++;
    j++;
}
return i==s.length;
};